Metal frame of image forming apparatus and image forming apparatus

ABSTRACT

A metal frame of an image forming apparatus includes a first support which includes a first metal plate and a second metal plate; a second support configured to support the image forming unit together with the first support; and a third support configured to connect the first support and the second support. The first metal plate includes a corner portion provided between a first portion and a second portion. The second metal plate includes a third portion, a fourth portion, and a fifth portion, wherein the fifth portion includes another corner portion located between a first stretched portion and a second stretched portion facing the corner portion of the first metal plate. A tip of the second stretched portion faces the fourth portion.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a metal frame of an image formingapparatus such as an electrophotographic copying machine and anelectrophotographic printer (for example, a laser beam printer or alight emitting diode (LED) printer).

Description of the Related Art

A frame of an image forming apparatus is generally formed by fixing aplurality of metal plates such as a front side plate, a rear side plate,and a stay connecting between the front side plate and the rear sideplate to each other by welding or the like. By fixing such metal platesto each other in a state where they are assembled to each other withhigh position accuracy, position accuracy between respective memberssupported by the frame is maintained, such that it becomes possible toform a high-quality image.

Meanwhile, Japanese Patent Application Laid-Open No. 2008-116619describes a configuration for assembling a first metal plate and asecond metal plate, which are metal plates constituting a frame of animage forming apparatus, to each other with high position accuracy. Theconfiguration described in Japanese Patent Application Laid-Open No.2008-116619 is a configuration in which a protrusion portion formed onthe first metal plate is inserted into an opening portion formed in thesecond metal plate to assemble the first metal plate and the secondmetal plate to each other. A first bulging portion that abuts on onesurface of the protrusion portion of the first metal plate in a platethickness direction and a second bulging portion that abuts on the othersurface of the first metal plate in the plate thickness direction areformed inside the opening portion of the second metal plate. By nippingthe protrusion portion from the plate thickness direction by the firstbulging portion and the second bulging portion, a position of the firstmetal plate with respect to the second metal plate in the platethickness direction is determined. In addition, in a directionorthogonal to an insertion direction of the first metal plate into thesecond metal plate and the plate thickness direction of the first metalplate, by making a width of the opening portion and a width of theprotrusion portion substantially the same as each other, a position ofthe first metal plate with respect to the second metal plate in theorthogonal direction is determined.

When two metal plates constituting the frame of the image formingapparatus are assembled and positioned, it is preferable that one metalplate can be easily assembled to the other metal plate. However, whenthe difference between the size of the opening and the plate thicknessand width of the protrusion portion is increased in order to realizethis, positioning accuracy between metal plates may decrease, andposition accuracy between each member supported by the frame maydeteriorate, adversely affecting image quality. As described above, inthe conventional configuration, in a configuration in which the metalplates engage with each other to be positioned, it was difficult toachieve both easy assembly and improvement of the positioning accuracy.

SUMMARY OF THE INVENTION

It is desirable to provide a metal frame of an image forming apparatusthat can achieve both easy assembly of two metal plates constituting ametal frame and improvement of positioning accuracy between the twometal plates.

A representative configuration of the present invention provides

a metal frame of an image forming apparatus, including:

a first support configured to support one end of an image forming unitthat forms an image on a sheet, the first support including a firstmetal plate and a second metal plate which supports the first metalplate below the first metal plate in a vertical direction;

a second support which is spaced apart from the first support andconfigured to support the other end of the image forming unit; and

a third support configured to connect the first support and the secondsupport to each other,

wherein the first metal plate includes

a first portion, and

a second portion which is bent substantially vertically from the firstportion, and including a substantially right-angled corner portion beingprovided between the first portion and the second portion,

wherein the second metal plate includes

a third portion,

a fourth portion which is bent substantially vertically upward in thevertical direction from an end portion in a first direction orthogonalto the vertical direction in the third portion, and engages with and isassembled to the first portion, and

a fifth portion which is bent substantially vertically upward in thevertical direction from an end portion in a second direction orthogonalto the vertical direction and the first direction in the third portion,and engages with and is assembled to the second portion,

wherein the fifth portion includes a first stretched portion whichextends along the end portion in the second direction with respect tothe third portion and a second stretched portion which is bentsubstantially vertical with respect to the first stretched portion andextends along the second direction, another corner portion locatedbetween the first stretched portion and the second stretched portionfacing the corner portion of the first metal plate, and

wherein a tip of the second stretched portion faces the fourth portion.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an image forming apparatus;

FIG. 2 is a schematic cross-sectional view of the image formingapparatus;

FIG. 3 is a perspective view of the frame of the image formingapparatus;

FIG. 4 is a perspective view of the frame of the image formingapparatus;

FIG. 5 is a perspective view when a rear bottom plate is assembled;

FIGS. 6A and 6B are perspective views when a rear side plate isassembled;

FIGS. 7A and 7B are perspective views of an engaging portion between therear bottom plate and the rear side plate;

FIG. 8 is a top view of the rear bottom plate;

FIGS. 9A to 9C are perspective views sequentially illustrating aprocessing method of the rear bottom plate;

FIGS. 10A and 10B are perspective views of the engaging portion betweenthe rear bottom plate and the rear side plate;

FIGS. 11A and 11B are perspective views of the engaging portion betweenthe rear bottom plate and the rear side plate;

FIGS. 12A and 12B are perspective views of the engaging portion betweenthe rear bottom plate and the rear side plate;

FIGS. 13A and 13B are perspective views when the rear side plate isassembled;

FIG. 14 is a perspective view of the engaging portion between the rearside plates;

FIG. 15 is a top view of the rear side plate;

FIGS. 16A to 16D are perspective views sequentially illustrating aprocessing method of the rear side plate;

FIGS. 17A and 17B are perspective views when a middle stay is assembled;

FIGS. 18A to 18C are perspective views when a front side plate isassembled;

FIGS. 19A and 19B are perspective views when a left support column isassembled;

FIGS. 20A and 20B are perspective views when a front lower stay isassembled;

FIG. 21 is a perspective view when a right support column is assembled;

FIGS. 22A and 22B are perspective views when a left lower stay isassembled;

FIGS. 23A and 23B are perspective views when a left upper stay isassembled;

FIG. 24 is a perspective view when a right lower stay is assembled;

FIGS. 25A and 25B are perspective views of the right lower stay, therear side plate, and the right support column;

FIG. 26 is a perspective view when the rear side plate is assembled;

FIGS. 27A and 27B are perspective views when a right middle stay isassembled;

FIG. 28 is a perspective view when a right support column is assembled;

FIGS. 29A and 29B are enlarged perspective views of an engaging portionbetween the right support column and the right support column;

FIGS. 30A and 30B are perspective views when a right upper stay isassembled;

FIG. 31 is a perspective view of a jig used for fixing the frame;

FIG. 32 is a perspective view of the frame and the jig; and

FIG. 33 is a perspective view of the frame and the jig.

DESCRIPTION OF THE EMBODIMENTS

<Image Forming Apparatus>

Hereinafter, an overall configuration of an image forming apparatusaccording to the present invention will be described with reference tothe drawings, together with an operation at the time of image formation.Note that dimensions, materials, shapes, relative arrangements, and thelike of components described below are not intended to limit the scopeof the present invention unless specifically stated otherwise.

An image forming apparatus A according to the present embodiment is anintermediate tandem type electrophotographic image forming apparatusthat transfers toners of four colors of yellow Y, magenta M, cyan C, andblack K to an intermediate transfer belt, and then transfers an image toa sheet to form the image. Note that in the following description, Y, M,C, and K are added as subscripts to members using the toners of therespective colors, but since configurations or operations of therespective members are substantially the same as each other except thatcolors of the toners used in the respective members are different fromeach other, the subscripts are appropriately omitted unless it isnecessary to distinguish the configurations or the operations of therespective members from each other.

FIG. 1 is a schematic perspective view of an image forming apparatus A.FIG. 2 is a schematic cross-sectional view of an image forming apparatusA. As illustrated in FIGS. 1 and 2 , the image forming apparatus Aincludes an image forming portion 44 that forms a toner image andtransfers the toner image to a sheet, a sheet feeding portion 43 thatfeeds the sheet toward the image forming portion 44, and a fixingportion 45 that fixes the toner image to the sheet. In addition, animage reading portion 41 that reads an image of an original is providedat an upper portion of the image forming apparatus A.

The image forming portion 44 includes a process cartridge 3: 3Y, 3M, 3C,and 3K, a laser scanner unit 15, and an intermediate transfer unit 49.The process cartridge 3, which is an example of the image forming unit,is configured to be detachably attached to the image forming apparatusA, and includes a photosensitive drum 6: 6Y, 6M, 6C, and 6K, a chargingroller 8: 8Y, 8M, 8C, and 8K, and a developing device 4: 4Y, 4M, 4C, and4K.

The intermediate transfer unit 49 includes a primary transfer roller 5:5Y, 5M, 5C, and 5K, an intermediate transfer belt 14, a secondarytransfer roller 28, a secondary transfer counter roller 23, a drivingroller 21, and a tension roller 22. The intermediate transfer belt 14 isstretched over the secondary transfer counter roller 23, the drivingroller 21, and the tension roller 22, the driving roller 21 rotates by adriving force of a motor (not illustrated), and the intermediatetransfer belt 14 circularly moves according to the rotation of thetension roller 22.

Next, an image forming operation by the image forming apparatus A willbe described. First, when an image forming job signal is input to acontroller (not illustrated), a sheet S stacked and stored in a sheetcassette 42 is sent out to a registration roller 9 by a feeding roller16. Next, the sheet S is sent into a secondary transfer portionincluding the secondary transfer roller 28 and the secondary transfercounter roller 23 at a predetermined timing by the registration roller9.

Meanwhile, in the image forming portion, first, a surface of thephotosensitive drum 6Y is charged by the charging roller 8Y. Then, thelaser scanner unit 15 irradiates the surface of the photosensitive drum6Y with laser light according to an image signal transmitted from anexternal device (not illustrated) or the like to form an electrostaticlatent image on the surface of the photosensitive drum 6Y.

Then, a yellow toner is attached to the electrostatic latent imageformed on the surface of the photosensitive drum 6Y by the developingdevice 4Y to form a yellow toner image on the surface of thephotosensitive drum 6Y. The toner image formed on the surface of thephotosensitive drum 6Y is primarily transferred to the intermediatetransfer belt 14 by applying a bias to the primary transfer roller 5Y.

Magenta, cyan, and black toner images are also formed on thephotosensitive drums 6M, 6C, and 6K by a similar process. These tonerimages are transferred in a superimposed manner onto the yellow tonerimage on the intermediate transfer belt 14 by applying a primarytransfer bias to the primary transfer rollers 5M, 5C, and 5K. As aresult, a full-color toner image is formed on a surface of theintermediate transfer belt 14.

Note that when the toner inside the developing device 4 is used by thedeveloping process described above, such that an amount of toner insidethe developing device 4 decreases, each developing device 4 isreplenished with a toner of each color by a toner bottle 32: 32Y, 32M,32C, and 32K. The toner bottle 32 is configured to be detachablyattachable to the image forming apparatus A.

Then, the intermediate transfer belt 14 circularly moves, such that afull-color toner image is sent to the secondary transfer portion. Thefull-color toner image on the intermediate transfer belt 14 istransferred to the sheet S by applying a bias to the secondary transferroller 28 in the secondary transfer portion.

Then, the sheet S to which the toner image is transferred is subjectedto heating and pressuring processing in the fixing portion 45, such thatthe toner image on the sheet S is fixed to the sheet S. Then, the sheetS to which the toner image is fixed is discharged to a discharge portion19 by a discharge roller 18.

<Frame of Image Forming Apparatus>

Next, a frame 31 (metal frame) of the image forming apparatus A will bedescribed.

FIG. 3 is a perspective view of the frame 31 of the image formingapparatus A when viewed from a front surface side of the image formingapparatus A, and is a perspective view of a state where an internal unitsuch as an image forming unit or an exterior cover is removed from theframe 31. FIG. 4 is a perspective view of the frame 31 of the imageforming apparatus A when viewed from a rear surface side of the imageforming apparatus A. Note that an arrow X direction illustrated in thedrawings is a horizontal direction and indicates a left and rightdirection of the image forming apparatus A. In addition, an arrow Ydirection is a horizontal direction and indicates a front and reardirection of the image forming apparatus A. In addition, an arrow Zdirection is a vertical direction and indicates an up and down directionof the image forming apparatus A. In addition, a front side of the imageforming apparatus A is a side on which a user normally stands in orderto operate an operation portion 46 for performing a setting regardingimage formation, and a rear side of the image forming apparatus A is aside opposite to the front side across the frame 31. In addition, a leftside of the image forming apparatus A is a left side when viewed fromthe front side, and a right side of the image forming apparatus A is aright side when viewed from the front side. In addition, the front sideof the image forming apparatus A is a direction in which the sheetcassette 42 is pulled out from the image forming apparatus A when thesheet cassette 42 is replenished with sheets, and is a direction inwhich the toner bottle 32 is pulled out when the toner bottle 32 isreplaced.

As illustrated in FIGS. 3 and 4 , the image forming apparatus Aincludes, as a second support, a front side plate 55 (third side plate),a left support column 56 (first support column), and a right supportcolumn 67 (second support column). The front side plate 55, the leftsupport column 56, and the right support column 67 are formed by metalplates, and are the frame 31 of the front side of the image formingapparatus A. The left support column 56 is connected to one end side ofthe front side plate 55 in the arrow X direction to support the frontside plate 55. The right support column 67 is connected to the other endside of the front side plate 55 in the arrow X direction to support thefront side plate 55. In addition, the right support column 67 includes aright support column 58 and a right support column 63 connected to anupper side of the right support column 58 in the vertical direction. Theleft support column 56 and the right support column 58 are connected toeach other by a front lower stay 57 and the front side plate 55.

Further, the image forming apparatus A includes, as a first support, arear side plate 50 and a rear bottom plate 51. the rear side plate 50and the rear bottom plate 51 are formed by metal plates, and are theframe 31 of the back side of the image forming apparatus A. The rearside plate 50 is arranged to face the front side plate 55, and supportsthe process cartridge 3 together with the front side plate 55. The rearside plate 50 is divided into three as a rear side plate 52, a rear sideplate 53, and a rear side plate 62 in the vertical direction, the rearside plate 53 (first side plate) is connected above the rear side plate52 (second side plate) in the vertical direction, and the rear sideplate 62 is connected above the rear side plate 53 in the verticaldirection. In addition, a thickness of the metal plate of each of therear side plates 52, 53, and 62 is about 0.6 mm to 2 mm.

In addition, the image forming apparatus A includes a left lower stay59, a left upper stay 60, a right lower stay 61, a right middle stay 65,a right upper stay 64, and a middle stay 54, as connecting memberconnecting the frame 31 on the front surface side and the frame 31 onthe rear surface side to each other. Here, the left lower stay 59, theleft upper stay 60, the right lower stay 61, the right middle stay 65,the right upper stay 64, and the middle stay 54 are example of a thirdsupport and a connecting member connecting the rear side plate 50constituting the rear surface of the frame 31 to the front side plate55, the left support column 56 and the right support column 67,constituting the front surface of the frame 31.

The left lower stay 59 connects the left support column 56 and the rearside plate 52 to each other. The left upper stay 60 connects the leftsupport column 56 and the rear side plate 53 to each other. The rightlower stay 61 connects the right support column 58 and the rear sideplate 52 to each other. The right middle stay 65 connects the rear sideplate 53 and the right support column 58 to each other. The right upperstay 64 connects the right support column 63 and the rear side plate 62to each other. The middle stay 54 connects the front side plate 55 andthe rear side plate 53 to each other.

Note that each of the members constituting the frame 31 described aboveis formed of one metal plate. These metal plates are processed into apredetermined shape by drawing or the like, temporarily assembled in anassembly process described later, and then fixed through a fixingprocess to form the frame 31.

<Frame Assembling Process>

Next, a process of assembling a plurality of metal plates constitutingthe frame 31 will be described. FIGS. 5 to 30 are views illustratingaspects where the metal plates constituting the frame 31 are assembled.

As illustrated in FIG. 5 , a stand 33 as a first jig is used when themetal plates constituting the frame 31 are assembled. The stand 33 has abase portion provided with positioning pins 33 a and 33 b, and a supportcolumn 33 c erected on the base portion. First, the rear bottom plate 51is placed on the stand 33.

The rear bottom plate 51 (second metal plate) is provided with a flatsurface portion 51 w 1 (third portion) that faces the stand 33 andextends in the horizontal direction. Further, the rear bottom plate 51includes a bent and raised portion 51 w 2 (fourth portion) and a bentand raised portion 51 w 3 in which one end portion and the other endportion in the arrow Y direction (first direction) orthogonal to thevertical direction (arrow Z direction) of the flat surface portion 51 w1 are bent substantially vertically (89° to 90°) upward in the verticaldirection, respectively. Further, the rear bottom plate 51 includes abent and raised portion 51 w 4 (fifth portion) and a bent and raisedportion 51 w 5 in which one end portion and the other end portion in thearrow X direction (second direction) orthogonal to the verticaldirection (arrow Z direction) and an arrow Y direction of the flatsurface portion 51 w 1 are bent substantially vertically (89° to 90°)upward in the vertical direction, respectively. The bent and raisedportions 51 w 2 to 51 w 5 are formed at least on a side engaging withthe rear side plate 52.

When the rear bottom plate 51 is placed on the stand 33, the positioningpin 33 a of the stand 33 is inserted into the positioning hole 51 aformed in the flat surface portion 51 w 1 of the rear bottom plate 51.As a result, the position of the rear bottom plate 51 with respect tothe stand 33 is determined.

Next, as illustrated in FIGS. 6A and 6B, the rear side plate 52 (firstmetal plate) is inserted into the rear bottom plate 51 from the verticaldirection (arrow Z direction) and assembled. The rear side plate 52 issubjected to bending so as to have a U-shape having three flat surfaces.The rear side plate 52 includes a flat surface portion 52 a (firstportion) located on the rear surface of the image forming apparatus Aand a bent portion 52 b (second portion) that is bent so that thebending angle is substantially vertical (89° to 91°) to the flat surfaceportion 52 a and extends to the rear of the image forming apparatus A.The flat surface portion 52 a and the bent portion 52 b form a cornerportion 52 h by bending. In addition, the rear side plate 52 includes abent portion 52 w bent with respect to the flat surface portion 52 a soas to face the bent portion 52 b.

The upper portion of the flat surface portion 52 a of the rear sideplate 52 is provided with a stepped portion 52 a 1 bent in the platethickness direction (arrow Y direction) of the flat surface portion 52 aso that a step is formed in the arrow Y direction with the flat surfaceportion 52 a. The upper portion of the bent portion 52 b of the rearside plate 52 is provided with a stepped portion 52 b 1 bent in theplate thickness direction (arrow X direction) of the bent portion 52 bso that a step is formed in the arrow X direction with the bent portion52 b. The upper portion of the bent portion 52 w of the rear side plate52 is provided with a stepped portion 52 w 1 bent in the plate thicknessdirection (arrow X direction) of the bent portion 52 w so that a step isformed in the arrow X direction with the bent portion 52 w.

As illustrated in FIG. 6B, the flat surface portion 52 a of the rearside plate 52 is provided with a projection portion 52 n formed so as toprotrude in the plate thickness direction by drawing. In addition, athrough-hole 51 n penetrating the bent and raised portion 51 w 2 in aplate thickness direction (arrow Y direction) of the bent and raisedportion 51 w 2 is formed in the bent and raised portion 51 w 2 of therear bottom plate 51. When the rear side plate 52 is assembled, theprojection portion 52 n of the rear side plate 52 engages with thethrough-hole 51 n of the rear bottom plate 51. As a result, an edgeportion 52 n 1 of the projection portion 52 n abuts on an inner wall ofthe through-hole 51 n, such that movement of the rear side plate 52 withrespect to the rear bottom plate 51 in a direction opposite to theinsertion direction is restricted.

FIGS. 7A and 7B are perspective view of a region U1 illustrated in FIGS.6A and 6B. Here, FIG. 7A illustrates a state before the rear side plate52 is assembled to the rear bottom plate 51. FIG. 7B illustrates a statebefore the rear side plate 52 is assembled to the rear bottom plate 51.FIG. 8 is a top view of the rear bottom plate 51 in the region U1illustrated in FIGS. 6A and 6B.

As illustrated in FIGS. 7 and 8 , a step-bent portion 52 m (firstengaging portion) is formed in the lower portion of the flat surfaceportion 52 a of the rear side plate 52. The step-bent portion 52 m has aportion (first bent portion) bent in the plate thickness direction(arrow Y direction) of the flat surface portion 52 a and a portion(second bent portion) bent and extended from that portion in aninsertion direction (arrow Z direction) of the rear bottom plate 51. Atip portion of the step-bent portion 52 m is an inclined portion 52 m 1inclined in a direction away from the flat surface portion 52 a of therear side plate 52 with respect to the insertion direction of the rearbottom plate 51 into the rear side plate 52.

In addition, a step-bent portion 52 p (second engaging portion) isprovided at a lower portion of the bent portion 52 b of the rear sideplate 52. The step-bent portion 52 p has a portion (third bent portion)bent in a plate thickness direction (arrow X direction) of the bentportion 52 b and a portion (fourth bent portion) bent and extended fromthat portion with respect to the insertion direction of the rear bottomplate 51. A tip portion of the step-bent portion 52 p is an inclinedportion 52 p 1 inclined in a direction away from the bent portion 52 bof the rear side plate 52 with respect to the insertion direction of therear side plate 52 into the rear bottom plate 51.

When the rear side plate 52 is assembled, the step-bent portions 52 mand 52 p of the rear side plate 52 engages with the bent and raisedportions 51 w 2 and 51 w 4 of the rear bottom plate 51. At this time,the inclined portions 52 m 1 and 52 p 1 of the rear side plate 52 abuton the bent and raised portions 51 w 2 and 51 w 4 of the rear bottomplate 51, such that movement of the rear side plate 52 in the arrow Zdirection is guided. As a result, the step-bent portion 52 m and theflat surface portion 52 a on the rear side plate 52 is sandwiched by thebent and raised portion 51 w 2 of the rear bottom plate 51 from theplate thickness direction, and the bent and raised portion 51 w 4 of therear bottom plate 51 is sandwiched by the step-bent portion 52 p and thebent portion 52 b from the plate thickness direction. In this way, thepositions of the rear side plate 52 with respect to the rear bottomplate 51 in the arrow X direction and the arrow Y direction aredetermined.

In addition, when the rear side plate 52 is inserted into the rearbottom plate 51 up to a position where a lower end portion of the rearside plate 52 abuts on a surface of the stand 33 on which the rearbottom plate 51 is placed or a position where portions of the step-bentportions 52 m and 52 p bent and raised from the flat surface portions 52a and the bent portion 52 b abut on an upper end portion of the bent andraised portion 51 w 2 of the rear bottom plate 51, positions of the rearside plate 52 and the rear bottom plate 51 in the arrow Z direction aredetermined, such that a final relative position between the rear bottomplate 51 and the rear side plate 52 is determined.

Further, the bent and raised portions 51 w 2 and 51 w 4 of the rearbottom plate 51 are provided with bent portions 51 j (second bentportion) and 51 k (first bent portion) that close at least a part of anotch portion 51 w 6 formed in the rear bottom plate 51. The notchportion 51 w 6 is a notch required for bending when forming the bent andraised portions 51 w 2 and 51 w 4 of the rear bottom plate 51.

The bent portion 51 j is formed by being bent substantially vertically(89° to 91°) in the arrow X direction from the end portion of the bentand raised portion 51 w 4 in the arrow Y direction toward the bent andraised portion 51 w 2. The bent portion 51 k is formed by being bentsubstantially vertically (89° to 91°) in the arrow Y direction from theend portion of the bent and raised portion 51 w 2 in the arrow Xdirection toward the bent and raised portion 51 w 4. A tip portion 51 j1 of the bent portion 51 j is a portion of the bent and raised portion51 w 4 closest to the bent and raised portion 51 w 2. In other words, aside surface portion 51 k 1 of the bent portion 51 k is a portion of thebent and raised portion 51 w 2 closest to the bent and raised portion 51w 4. A gap V1 between the tip portion 51 j 1 of the bent portion 51 jand the side surface portion 51 k 1 of the bent portion 51 k illustratedin FIG. 8 is equal to or less than a thickness of the bent portion 52 bof the rear side plate 52. It should be noted that the bent portion 51 jand the bent portion 51 k may be brought into contact with each otherwithout providing the gap V1. The bent and raised portion 51 w 4 is anexample of a first extending portion extending in the arrow Y direction,and the bent portion 51 j is an example of a second extending portionextending in the arrow X direction bent with respect to the bent andraised portion 51 w 4. In addition, the bent and raised portion 51 w 2is an example of a third extending portion extending in the arrow Xdirection, and the bent portion 51 k is an example of a fourth extendingportion extending in the arrow Y direction substantially bentright-angled with respect to the bent and raised portion 51 w 2.

FIGS. 9A to 9C are perspective views illustrating a processing method ofthe bent and raised portions 51 w 2 and 51 w 4 and the bent portions 51j and 51 k in order. As illustrated in FIGS. 9A and 9B, when forming thebent and raised portions 51 w 2 and 51 w 4 and the bent portions 51 jand 51 k, first, the bent portions 51 j and 51 k are formed by bendingthe corner portions around the notch portion 51 w 6 on the rear bottomplate 51 almost vertically upward in the vertical direction,respectively. Next, as illustrated in FIG. 9C, one end portion of theflat surface portion 51 w 1 in the arrow X direction and one end portionin the arrow Y direction are bent substantially vertically upward in thevertical direction to form the bent and raised portions 51 w 2 and 51 w4, respectively. In this way, the bent and raised portions 51 w 2 and 51w 4 and the bent portions 51 j and 51 k are bent.

When the rear side plate 52 is assembled to the rear bottom plate 51,the following effects are obtained by providing the rear bottom plate 51with bent portions 51 j and 51 k. That is, as illustrated in FIG. 10A,in the case where the bent portion 51 j is not provided, when the rearside plate 52 is inserted into the rear bottom plate 51, the cornerportion 52 h of the rear side plate 52 enters a space above the notchportion 51 w 6, and thus, there is a possibility that both the bentportion 52 b and the step-bent portion 52 p of the rear side plate 52are inserted into one side of the rear bottom plate 51 with respect tothe bent and raised portion 51 w 4. In this case, since the step-bentportion 52 p does not engage and the bent and raised portion 51 w 4 ofthe rear bottom plate 51 cannot be sandwiched between the bent portion52 b and the step-bent portion 52 p of the rear side plate 52, therelative position accuracy between the rear bottom plate 51 and the rearside plate 52 deteriorates.

On the other hand, as illustrated in FIG. 10B, the rear bottom plate 51is provided with the bent portion 51 j so the rear side plate 52 isinserted into the rear bottom plate 51 at the above-described erroneousposition, the lower end portion of the bent portion 52 b of the rearside plate 52 interferes with the bent portion 51 j of the rear bottomplate 51. Therefore, the rear side plate 52 cannot be inserted into therear bottom plate 51 to the end. Therefore, it is possible to preventthe rear side plate 52 from being assembled at an erroneous positionwith respect to the rear bottom plate 51, and to prevent the relativeposition accuracy between the rear bottom plate 51 and the rear sideplate 52 from deteriorating.

In addition, as illustrated in FIG. 11A, in the case where the bentportion 51 k is not provided, when the rear side plate 52 is insertedinto the rear bottom plate 51, the corner portion 52 h of the rear sideplate 52 enters a space above the notch portion 51 w 6, and thus, thereis a possibility that both the flat surface portion 52 a and thestep-bent portion 52 m of the rear side plate 52 are inserted into oneside of the bent and raised portion 51 w 2. In this case, the step-bentportion 52 m does not engage, and the flat surface portion 52 a and thestep-bent portion 52 m of the rear side plate 52 cannot sandwich thebent and raised portion 51 w 2 of the rear bottom plate 51, so therelative position accuracy between the rear bottom plate 51 and the rearside plate 52 deteriorates.

On the other hand, as illustrated in FIG. 11B, the rear bottom plate 51is provided with the bent portion 51 k so the rear side plate 52 isinserted into the rear bottom plate 51 at the above-described erroneousposition, the lower end portion of the flat surface portion 52 a of therear side plate 52 interferes with the bent portion 51 k of the rearbottom plate 51. Therefore, the rear side plate 52 cannot be insertedinto the rear bottom plate 51 to the end. Therefore, it is possible toprevent the rear side plate 52 from being assembled at an erroneousposition with respect to the rear bottom plate 51, and to prevent therelative position accuracy between the rear bottom plate 51 and the rearside plate 52 from deteriorating.

That is, in order to secure the strength of the rear bottom plate 51 andto assemble the rear side plate 52, the rear bottom plate 51 needs to beprovided with the bent and raised portions 51 w 2 to 51 w 5. In order tobend the bent and raised portion 51 w 2 to 51 w 5, a notch such as thenotch portion 51 w 6 is required. When the notch portion 51 w 6 is leftas it is, as illustrated in FIGS. 10A and 11A, the rear side plate 52enters the space above the notch portion 51 w 6, and thus, there is apossibility that the rear side plate 52 is assembled at the erroneousposition.

On the other hand, the bent portions 51 j and 51 k are provided to closeat least a part of the notch portion 51 w 6, and when viewed from thevertical direction, the portion of the bent and raised portion 51 w 4that comes into contact with or is closest to the bent and raisedportion 51 w 2 is arranged at a position different from the cornerportion 52 h of the rear side plate 52. With such a configuration, whenthe rear side plate 52 is to be assembled at the above-describederroneous position, the bent and raised portions 51 w 2 and 51 w 4interfere with the rear side plate 52 to restrict the assembly, so it ispossible to prevent the rear side plate 52 from being assembled at theerroneous position. Therefore, according to the configuration of thepresent embodiment, it is possible to achieve both ease of assembly ofthe rear bottom plate 51 and the rear side plate 52, which are the twometal plates constituting the frame 31, and improve positioningaccuracy.

Although the present embodiment has described a configuration in whichat least a part of the notch portion 51 w 6 is closed by the two bentportions 51 j and 51 k of the rear bottom plate 51 to prevent the rearside plate 52 from being inserted into an erroneous position, thepresent invention is not limited thereto. That is, as long as whenviewed from the vertical direction, the portion that comes in contactwith or closest to the bent and raised portion 51 w 2 in the bent andraised portion 51 w 4 is arranged at a position different from thecorner portion 52 h of the rear side plate 52, the same effect asdescribed above can be obtained. For example, the configurationillustrated in FIG. 12A in which the notch portion 51 w 6 is closed byone bent portion 51 j, or the configuration illustrated in FIG. 12B inwhich the notch portion 51 w 6 is closed by one bent portion 51 k may beused.

Next, as illustrated in FIGS. 13A and 13B, the rear side plate 53supporting the process cartridge 3 is inserted into the rear side plate52 from the vertical direction (arrow Z direction) and assembled. Therear side plate 53 is subjected to bending so as to have a U-shapehaving three flat surfaces. The rear side plate 53 is located on therear surface of the image forming apparatus A, and includes a supportportion 53 a supporting the process cartridge 3 and a bent portion 53 bbent at a bending angle of a substantially right angle (89° to 91°) withrespect to the support portion 53 a and extending rearward of the imageforming apparatus A. The support portion 53 a and the bent portion 53 bform a corner portion 53 h by bending. In addition, the rear side plate53 includes a bent portion 53 w bent with respect to the support portion53 a so as to face the bent portion 53 b.

The support portion 53 a (first portion) of the rear side plate 53(first metal plate) is arranged to be adjacent to the flat surfaceportion 52 a in the vertical direction with respect to the flat surfaceportion 52 a (third portion) of the rear side plate 52 (second metalplate). In addition, the bent portion 53 b (second portion) of the rearside plate 53 is arranged above the bent portion 52 b (fourth portion)of the rear side plate 52 so as to be adjacent to the bent portion 52 b.Further, the bent portion 53 w of the rear side plate 53 is arranged soas to be adjacent to the bent portion 52 w in the vertical directionwith respect to the bent portion 52 w of the rear side plate 52.

As illustrated in FIG. 13B, the lower portion of the support portion 53a of the rear side plate 53 is provided with a projection portion 53 iformed so as to protrude in the plate thickness direction by drawing.Further, a through-hole 52 i penetrating in the plate thicknessdirection (arrow Y direction) is formed in the stepped portion 52 a 1 ofthe rear side plate 52. When the rear side plate 53 is assembled, theprojection portion 53 i of the rear side plate 53 engages with thethrough-hole 52 i of the rear side plate 52. As a result, an edgeportion 53 i 1 of the projection portion 53 i abuts on an inner wall ofthe through-hole 52 i, such that movement of the rear side plate 53 withrespect to the rear side plate 52 in a direction opposite to theinsertion direction is restricted.

FIG. 14 is a perspective view of a region U2 illustrated in FIGS. 13Aand 13B. Here, FIG. 14A illustrates a state before the rear side plate52 is assembled to the rear bottom plate 51. FIG. 14B illustrates astate before the rear side plate 52 is assembled to the rear bottomplate 51. FIG. 15 is a top view of the rear side plate 52 in the regionU2 illustrated in FIGS. 13A and 13B.

As illustrated in FIGS. 14 and 15 , a step-bent portion 53 m (firstengaging portion) is formed in the lower portion of the support portion53 a of the rear side plate 53. The step-bent portion 53 m has a portion(first bent portion) bent in the plate thickness direction (arrow Ydirection) of the support portion 53 a and a portion (second bentportion) bent and extended from that portion in an insertion direction(arrow Z direction) of the rear side plate 52. A tip portion of thestep-bent portion 53 m is an inclined portion 53 m 1 inclined in adirection away from the support portion 53 a of the rear side plate 53with respect to the insertion direction of the rear side plate 52 intothe rear side plate 53.

In addition, a step-bent portion 53 p (second engaging portion) and astopper portion 53 r are provided at a lower portion of the bent portion53 b of the rear side plate 53. The stopper portion 53 r is formed bypress working and protrudes from the bent portion 53 b in the arrow Xdirection. The step-bent portion 53 p has a portion (third bent portion)bent in a plate thickness direction (arrow X direction) of the bentportion 53 b and a portion (fourth bent portion) bent and extended fromthat portion in the insertion direction of the rear side plate 52. A tipportion of the step-bent portion 53 p is an inclined portion 53 p 1inclined in a direction away from the bent portion 53 b of the rear sideplate 53 with respect to the insertion direction of the rear side plate52 into the rear side plate 53.

When the rear side plate 53 is assembled, the step-bent portions 53 mand 53 p of the rear side plate 53 engage with step-bent portion 52 a 1(fifth portion) and 52 b 1 (sixth portion) of the rear side plate 52. Atthis time, the inclined portions 53 m 1 and 53 p 1 of the rear sideplate 53 abut on the stepped portions 52 a 1 and 52 b 1 of the rear sideplate 52, such that movement of the rear side plate 53 in the arrow Zdirection is guided. As a result, the stepped portion 52 a 1 of the rearside plate 52 is sandwiched by the step-bent portion 53 m and thesupport portion 53 a on the rear side plate 53 from the plate thicknessdirection, and the stepped portion 52 b 1 of the rear side plate 52 issandwiched by the step-bent portion 53 p and the bent portion 53 b fromthe plate thickness direction. In this way, the positions of the rearside plate 53 with respect to the rear side plate 52 in the arrow Xdirection and the arrow Y direction are determined.

In addition, when the stopper portion 53 r of the rear side plate 53 isinserted into a position where the stopper portion 53 r abuts on theupper end portion of the stepped portion 52 b 1 of the rear side plate52, the positions of the rear side plate 53 with respect to the rearside plate 52 in the arrow Z direction of the rear side plate 53 and therear side plate 52 are determined. In this way, the final relativeposition between the rear side plate 53 and the rear side plate 52 isdetermined.

Further, the stepped portions 52 a 1 and 52 b 1 of the rear side plate52 are provided with bent portions 52 j (second bent portion) and 52 k(first bent portion) that close at least a part of the notch portion 52r formed in the rear side plate 52. The notch portion 52 r is a notchrequired for bending when forming the stepped portions 52 a 1 and 52 b 1of the rear side plate 52.

The bent portion 52 j is formed by being bent substantially vertically(89° to 91°) in the arrow X direction from the end portion of thestepped portion 52 a 1 in the arrow Y direction toward the steppedportion 52 b 1. The bent portion 52 k is formed by being bentsubstantially vertically (89° to 91°) in the arrow Y direction from theend portion of the stepped portion 52 a 1 in the arrow X directiontoward the stepped portion 52 b 1. A tip portion 52 k 1 of the bentportion 52 k is the portion closest to the stepped portion 52 b 1 in thestepped portion 52 a 1. In other words, the side surface portion 52 j 1of the bent portion 52 j is the portion closest to the stepped portion52 a 1 in the stepped portion 52 b 1. A gap V2 between the tip portion52 k 1 of the bent portion 52 k and the side surface portion 52 j 1 ofthe bent portion 52 j illustrated in FIG. 15 is equal to or less thanthe thickness of the support portion 53 a of the rear side plate 53. Itshould be noted that the bent portion 52 j and the bent portion 52 k maybe brought into contact with each other without providing the gap V2.

FIGS. 16A to 16D are perspective views illustrating the processingmethod of the stepped portions 52 a 1 and 52 b 1 and the bent portions52 j and 52 k in order. As illustrated in FIGS. 16A and 16B, whenforming the stepped portions 52 a 1 and 52 b 1 and the bent portions 52j and 52 k, first, the bent portions 52 j and 52 k are formed bysubstantially vertically bending the corner portions around the notchportion 52 r on the rear side plate 52 in the arrow Y direction,respectively. Next, as illustrated in FIG. 16C, the upper portions ofthe flat surface portion 52 a and the bent portion 52 b in the verticaldirection are bent in the direction of the arrow Y to form steppedportions 52 a 1 and 52 b 1, respectively. Thereafter, as illustrated inFIG. 16D, the end portion of the flat surface portion 52 a in the arrowX direction is bent substantially vertically in the direction of thearrow Y to form the bent portion 52 b. In this way, the bent and raisedportions 51 w 2 and 51 w 4 and the bent portions 51 j and 51 k are bent.

When the rear side plate 53 is assembled to the rear side plate 52, thefollowing effects are obtained by providing the rear side plate 52 withbent portions 52 j and 52 k. That is, in the case where the bent portion52 j is not provided, when the rear side plate 53 is inserted into therear side plate 52, the corner portion 53 h of the rear side plate 53enters the space above the notch portion 52 r, and thus, there is apossibility that both the bent portion 53 b and the step-bent portion 53p of the rear side plate 53 may be inserted into one side of the rearside plate 52 with respect to the stepped portion 52 b 1. In this case,the step-bent portion 53 p does not engage, and the stepped portion 52 b1 of the rear side plate 52 cannot be sandwiched between the bentportion 53 b of the rear side plate 53 and the step-bent portion 53 p,so the relative position accuracy between the rear side plate 52 and therear side plate 53 deteriorates.

On the other hand, when the rear side plate 52 is provided with the bentportion 52 j so that the rear side plate 53 is inserted into the rearside plate 52 at the above-described erroneous position, the lower endportion of the bent portion 53 b of the rear side plate 53 interfereswith the bent portion 52 j of the rear side plate 52. Therefore, therear side plate 53 cannot be inserted into the rear side plate 52 to theend. Therefore, it is possible to prevent the rear side plate 53 frombeing assembled at an erroneous position with respect to the rear sideplate 52, and to prevent the relative position accuracy between the rearside plate 53 and the rear side plate 52 from deteriorating.

In addition, in the case where the bent portion 52 k is not provided,when the rear side plate 53 is inserted into the rear side plate 52, thecorner portion 53 h of the rear side plate 53 enters the space above thenotch portion 52 r, and thus, there is a possibility that both thesupport portion 53 a and the step-bent portion 53 m of the rear sideplate 53 is inserted into one side with respect to the stepped portion52 a 1. In this case, the step-bent portion 53 m does not engage, andthe stepped portion 52 a 1 of the rear side plate 52 cannot besandwiched between the support portion 53 a of the rear side plate 53and the step-bent portion 53 m, so the relative position accuracybetween the rear side plate 52 and the rear side plate 53 deteriorates.

On the other hand, when the rear side plate 52 is provided with the bentportion 52 k so that the rear side plate 53 is inserted into the rearside plate 52 at the above-described erroneous position, the lower endportion of the support portion 53 a of the rear side plate 53 interfereswith the bent portion 52 k of the rear side plate 52. Therefore, therear side plate 53 cannot be inserted into the rear side plate 52 to theend. Therefore, it is possible to prevent the rear side plate 53 frombeing assembled at an erroneous position with respect to the rear sideplate 52, and to prevent the relative position accuracy between the rearside plate 53 and the rear side plate 52 from deteriorating.

That is, in order to secure the strength of the rear side plate 52, andto align the positions of the flat surface portion 52 a of the rear sideplate 52 and the support portion 53 a of the rear side plate 53, and thepositions of the bent portion 52 b of the rear side plate 52 and thebent portion 53 b of the rear side plate 53, the stepped portions 52 a 1and 52 b 1 are required for the rear side plate 52. In order to bend thestepped portion 52 a 1 and 52 b 1, the notch such as the notch portion52 r is required. When the notch portion 52 r is left as it is, asdescribed above, the rear side plate 53 may enter the space above thenotch portion 52 r, and the rear side plate 53 may be assembled at anerroneous position.

On the other hand, the bent portions 52 j and 52 k are provided to closeat least a part of the notch portion 52 r, and when viewed from thevertical direction, the portion in contact with or closest to thestepped portion 52 a 1 in the stepped portion 52 b 1 is arranged at aposition different from the corner portion 53 h of the rear side plate53. With such a configuration, when the rear side plate 53 is to beassembled at the above-described erroneous position, the steppedportions 52 a 1 and 52 b 1 interfere with the rear side plate 53 torestrict the assembly, so it is possible to prevent the rear side plate53 from being assembled at the erroneous position. Therefore, accordingto the configuration of the present embodiment, it is possible toachieve both ease of assembly of the rear side plate 52 and the rearside plate 53, which are the two metal plates constituting the frame 31,and improve positioning accuracy.

Although the present embodiment has described a configuration in whichat least a part of the notch portion 52 r is closed by the two bentportions 52 j and 52 k of the rear side plate 52 to prevent the rearside plate 53 from being inserted into an erroneous position, thepresent invention is not limited thereto. That is, as long as theportion in contact with or closest to the stepped portion 52 a 1 in thestepped portion 52 b 1 when viewed from the vertical direction isarranged at a position different from the corner portion 53 h of therear side plate 53, the same effect as described above can be obtained.For example, similar to the bent portion 51 j of the rear bottom plate51 illustrated in FIG. 12A, one bent portion 52 j may be configured tobe close to the notch portion 52 r, or similar to the bent portion 51 kof the rear bottom plate 51 illustrated in FIG. 12B, the notch portion52 r may be configured to be closed by one bent portion 52 k.

Next, as illustrated in FIGS. 17A and 17B, the middle stay 54 isassembled. The middle stay 54 is an optical stand on which the laserscanner unit 15 is placed, and is one example of the connecting member.The middle stay 54 is arranged on two support columns 33 c provided onthe stand 33, and is inserted into the support portion 53 a of the rearside plate 53. In the present embodiment, the middle stay 54 is a memberthat supports the laser scanner unit 15, but may be a member thatconnects the front side plate 55 and the rear side plate 50 at apredetermined distance at a position between the laser scanner unit 15and the sheet cassette 42 in the vertical direction. Further, if it isan exposure unit that exposes the photosensitive drum 6 by an LEDinstead of the laser scanner unit 15, the configuration may be such thatit is provided between the exposure unit and the sheet cassette 42 inthe vertical direction.

The middle stay 54 has a flat surface portion 54 w 1 extending in thehorizontal direction, and a bent and raised portion 54 w 2 bent andraised vertically and upward from the flat surface portion 54 w 1 at oneend portion of the flat surface portion 54 w 1 in the arrow Y direction.In addition, the middle stay 54 has a bent and raised portion 54 w 3bent vertically from the flat surface portion 54 w 1 so as to face thebent and raised portion 54 w 2 and a bent and raised portion 54 w 4 bentvertically and upward from the flat surface portion 54 w 1 at one endportion of the flat surface portion 54 w 1 in the arrow X direction. Inaddition, the middle stay 54 has a bent portion 54 w 5 bent verticallyand downward from the flat surface portion 54 w 1 at the other endportion of the flat surface portion 54 w 1 in the arrow X direction andfurther extending in the horizontal direction. The bent and raisedportion 54 w 4 of the middle stay 54 is provided with a protrusionportion 54 a protruding in an insertion direction (arrow Y direction)into the rear side plate 53. The protrusion portion 54 a of the middlestay 54 is inserted into a through-hole 150 formed in the supportportion 53 a of the rear side plate 53 and penetrating the supportportion 53 a in a plate thickness direction (arrow Y direction) of thesupport portion 53 a. As a result, a position of the middle stay 54 withrespect to the rear side plate 53 in the arrow X direction and the arrowY direction is determined.

Next, as illustrated in FIGS. 18A to 18C, the front side plate 55 isassembled. The middle stay 54 is inserted into the front side plate 55.The front side plate 55 has a flat surface portion 55 w 1 extending inthe vertical direction and a bent and raised portion 55 w 2 formed bybending and raising each of both end portions of the flat surfaceportion 55 w 1 in the arrow X direction and the arrow Y directionforward of the image forming apparatus A. Through-holes 55 a and 55 bpenetrating in the plate thickness direction (arrow Y direction) thereofis formed in the flat surface portion 55 w 1 of the front side plate 55.In addition, the bent and raised portion 54 w 3 of the middle stay 54 isprovided with protrusion portions 54 b and 54 c protruding in aninsertion direction (arrow Y direction) into the front side plate 55. Atip portion of the protrusion portion 54 b is provided with a hookportion 54 b 1 protruding upward of a base end portion.

The protrusion portion 54 b of the middle stay 54 is inserted into thethrough-hole 55 a formed in the flat surface portion 55 w 1 of the frontside plate 55, and the protrusion portion 54 c of the middle stay 54 isinserted into the through-hole 55 b formed in the flat surface portion55 w 1 of the front side plate 55. As a result, a position of the frontside plate 55 with respect to the middle stay 54 is determined. Inaddition, the hook portion 54 b 1 of the protrusion portion 54 b facesan upper portion of the through-hole 55 a in the front side plate 55. Asa result, the hook portion 54 b 1 of the middle stay 54 abuts on theflat surface portion 55 w 1 of the front side plate 55, such thatmovement of the middle stay 54 with respect to the front side plate 55in a direction opposite to the insertion direction is restricted and themiddle stay 54 is prevented from being separated.

Next, as illustrated in FIGS. 19A and 19B, the left support column 56 isassembled. The left support column 56 is arranged on the stand 33. Inaddition, the front side plate 55 is inserted into the left supportcolumn 56. The left support column 56 is mainly formed of two flatsurfaces, and has a flat surface portion 56 w 1 extending in parallelwith the flat surface portion 55 w 1 of the front side plate 55 and aflat surface portion 56 w 2 bent substantially vertically from the flatsurface portion 56 w 1 rearward of the image forming apparatus A. Athrough-hole 56 a penetrating in the arrow Y direction is provided atthe bent portion of the boundary between the flat surface portion 56 w 1and the flat surface portion 56 w 2 of the left support column 56. Inaddition, the flat surface portion 56 w 2 of the left support column 56is provided with a through-hole 56 b penetrating the flat surfaceportion 56 w 2 in a plate thickness direction (arrow X direction) of theflat surface portion 56 w 2. In addition, the bent and raised portion 55w 2 of the front side plate 55 is provided with protrusion portions 55 cprotruding in an insertion direction (arrow Y direction) into the leftsupport column 56 and a projection portion 55 d protruding in a platethickness direction (arrow X direction).

The protrusion portion 55 c of the front side plate 55 is inserted intothe through-hole 56 a formed in the left support column 56. As a result,a position of the left support column 56 with respect to the front sideplate 55 is determined. In addition, the projection portion 55 d of thefront side plate 55 engages with the through-hole 56 b of the leftsupport column 56. As a result, an edge portion 55 d 1 of the projectionportion 55 d abuts on an inner wall of the through-hole 56 b, such thatmovement of the front side plate 55 with respect to the left supportcolumn 56 in a direction opposite to the insertion direction isrestricted.

Next, as illustrated in FIGS. 20A and 20B, the front lower stay 57 isassembled. The front lower stay 57 is arranged on the stand 33, and isinserted and assembled into the left support column 56. The front lowerstay 57 has a flat surface portion 57 w 1, which is a flat surface to beplaced on the stand 33, and a bent and raised portion 57 w 2 formed bybending and raising each of both end portions of the flat surfaceportion 57 w 1 in the arrow X direction and the arrow Y directionsubstantially vertically and upward from the flat surface portion 57 w1. The bent and raised portion 57 w 2 of the front lower stay 57 isprovided with a protrusion portion 57 a protruding in an insertiondirection (arrow X direction) into the left support column 56.Positioning holes 57 b penetrating the flat surface portion 57 w 1 in aplate thickness direction (arrow Z direction) of the flat surfaceportion 57 w 1 are formed in the flat surface portion 57 w 1 of thefront lower stay 57. In addition, the flat surface portion 56 w 2 of theleft support column 56 is provided with a through-hole 56 c penetratingthe flat surface portion 56 w 2 in a plate thickness direction (arrow Xdirection) of the flat surface portion 56 w 2. Here, the width of theupper end portion of the through-hole 56 c is L1 and the width of thelower end portion is L2. In addition, the width of the tip portion ofthe protrusion portion 57 a is L3, and the width of the substrateportion is L4. At this time, the relationship is L1>L2, L4<L3, L1 L3,and L2≈L4.

The protrusion portion 57 a of the front lower stay 57 is inserted intoand engaged with a through-hole 56 c formed in the flat surface portion56 w 2 of the left support column 56. At this time, the protrusionportion 57 a is inserted from an upper side of the through-hole 56 c,and then moved to the lower end portion of the through-hole 56 c by theforce or gravity of an assembly operator. Here, when the protrusionportion 57 a is located at a lower end portion of the through-hole 56 c,movement of the protrusion portion 57 a with respect to the through-hole56 c in a direction opposite to the insertion direction is restricted bythe relationship of L3>L2. In addition, when the front lower stay 57 isarranged on the stand 33, the positioning pins 33 b of the stand 33 areinserted into the positioning holes 57 b of the front lower stay 57. Asa result, a position of the front lower stay 57 with respect to thestand 33 is determined.

Next, as illustrated in FIG. 21 , the right support column 58 isassembled. The right support column 58 is arranged on the stand 33. Inaddition, the front side plate 55 is inserted and assembled into theright support column 58. The right support column 58 has a flat surfaceportion 58 w 1 extending in parallel with the flat surface portion 55 w1 of the front side plate 55 and a flat surface portion 58 w 2 bentsubstantially vertically from the flat surface portion 58 w 1 forward ofthe image forming apparatus A. An assembly configuration of the rightsupport column 58 and the front side plate 55 is similar to that of theleft support column 56 and the front side plate 55. That is, athrough-hole (not illustrated) penetrating a bent portion of a boundarybetween the flat surface portion 58 w 1 and the flat surface portion 58w 2 of the right support column 58 in the arrow Y direction is formed inthe bend portion. A protrusion portion (not illustrated) formed in thebent and raised portion 55 w 2 of the front side plate 55 and protrudingin an insertion direction (arrow Y direction) into the right supportcolumn 58 is inserted into this through-hole. In addition, the flatsurface portion 58 w 2 of the right support column 58 is provided with athrough-hole (not illustrated) penetrating the flat surface portion 58 w2 in a plate thickness direction (arrow X direction) of the flat surfaceportion 58 w 2. A projection portion (not illustrated) formed in thebent and raised portion 55 w 2 of the front side plate 55 and protrudingin the arrow X direction engages with this through-hole. Here, the leftsupport column 56 and the right support column 58 are assembled afterassembling the front side plate 55 to the middle stay 54, but the frontside plate 55 is attached to the middle stay 54 with the left supportcolumn 56 mounted on the stand 33 in the order of assembling to the leftsupport column 56.

At a point in time when the frame 31 is assembled up to now, the frame31 can stand for oneself. That is, the frame 31 can stand for oneself byassembling the front side plate 55, the right support column 58, theleft support column 56, the front lower stay 57, which are the frame 31on the front surface side of the image forming apparatus A, the rearbottom plate 51 and the rear side plates 52 and 53, which are the frameon the rear surface side of the image forming apparatus A, and themiddle stay 54, which is the frame 31 connecting the frame on the frontsurface side and the frame on the rear surface side to each other, toeach other.

Next, as illustrated in FIGS. 22A and 22B, the left lower stay 59 isassembled. The left lower stay 59 has a flat surface portion 59 w 1extending in parallel with the flat surface portion 56 w 2 of the leftsupport column 56, and a bent and raised portion 59 w 2 bent in theplate thickness direction (arrow X direction) of the flat surfaceportion 59 w 1 at the upper part of the flat surface portion 59 w 1. Theleft lower stay 59, and the rear side plate 52 and the left supportcolumn 56 are inserted and assembled into each other from the verticaldirection. An assembly configuration of the left lower stay 59 and theleft support column 56 and an assembly configuration of the left lowerstay 59 and the rear side plate 52 are similar to each other. Therefore,only the assembly configuration of the left lower stay 59 and the leftsupport column 56 will be described here.

The flat surface portion 56 w 2 of the left support column 56 isprovided with a protrusion portion 56 g and a step-bent portion 56 jthat protrude in an insertion direction (arrow Z direction) into theleft lower stay 59 and a projection portion 56 h that protrudes in aplate thickness direction (arrow X direction) of the flat surfaceportion 56 w 2. The step-bent portion 56 j has a portion bent in theplate thickness direction of the flat surface portion plate 56 w 2 and aportion bent and extended from that portion in the insertion directioninto the left lower stay 59. In addition, a tip portion of the step-bentportion 56 j is an inclined portion 56 j 1 inclined in a direction awayfrom the flat surface portion 56 w 2 with respect to the insertiondirection of the left support column 56 into the left lower stay 59. Inaddition, a through-hole 59 a penetrating the flat surface portion 59 w1 in the plate thickness direction (arrow X direction) of the flatsurface portion 59 w 1 and a notch portion 59 b notched in the flatsurface direction are formed in the flat surface portion 59 w 1 of theleft lower stay 59.

The protrusion portion 56 g of the left support column 56 is insertedinto and engaged with the through-hole 59 a formed in the flat surfaceportion 59 w 1 of the left lower stay 59. Here, the width of theprotrusion portion 56 g in the arrow Y direction and the width of thethrough-hole 59 a in the arrow Y direction are almost the same.Therefore, the protrusion portion 56 g is inserted into the through-hole59 a, such that a position of the left lower stay 59 with respect to theleft support column 56 in the arrow Y direction is determined.

In addition, the step-bent portion 56 j of the left support column 56 isinserted into and engaged with a lower end portion of the flat surfaceportion 59 w 1 of the left lower stay 59. As a result, the flat surfaceportion 59 w 1 of the left lower stay 59 is sandwiched from the platethickness direction (arrow X direction) of the flat surface portion 59 w1 by the step-bent portion 56 j and the flat surface portion 56 w 2 inthe left support column 56, such that a position of the left lower stay59 with respect to the left support column 56 in the arrow X directionis determined.

In addition, the projection portion 56 h of the left support column 56engages with the notch portion 59 b formed in the left lower stay 59. Asa result, an edge portion 56 h 1 of the projection portion 56 h abuts onan inner wall of the notch portion 59 b, such that movement of the leftsupport column 56 with respect to the left lower stay 59 in a directionopposite to the insertion direction is restricted.

Next, as illustrated in FIGS. 23A and 23B, the left upper stay 60 isassembled. The left lower stay 59, and the rear side plate 53 and theleft support column 56 are inserted and assembled into each other fromthe vertical direction. An assembly configuration of the left upper stay60 and the rear side plate 53 and an assembly configuration of the leftupper stay 60 and the left support column 56 are similar to each other.Therefore, only the assembly configuration of the left upper stay 60 andthe left support column 56 will be described here.

A protrusion portion 56 d and a step-bent portion 56 e that protrude inan insertion direction (arrow Z direction) into the left upper stay 60are formed in the flat surface portion 56 w 2 of the left support column56. The step-bent portion 56 e has a portion bent in the plate thicknessdirection (arrow X direction) of the flat surface portion plate 56 w 2of the left support column 56 and a portion bent and extended from thatportion in the insertion direction into the left upper stay 60. Inaddition, a tip portion of the step-bent portion 56 e is an inclinedportion 56 e 1 inclined in a direction away from the flat surfaceportion 56 w 2 with respect to the insertion direction of the leftsupport column 56 into the left upper stay 60.

The left upper stay 60 has a flat surface portion 60 w 1 extending inparallel with the flat surface portion 56 w 2 of the left support column56, and a bent and raised portion 60 w 2 bent in the plate thicknessdirection (arrow X direction) of the flat surface portion 60 w 1 at theupper part of the flat surface portion 60 w 1. Through-hole 60 a and 60b penetrating the flat surface portion 60 w 1 in the plate thicknessdirection (arrow X direction) thereof is formed in the flat surfaceportion 60 w 1 of the left upper stay 60.

The protrusion portion 56 d of the left support column 56 is insertedinto and engaged with the through-hole 60 a formed in the flat surfaceportion 60 w 1 of the left upper stay 60. Here, the width of theprotrusion portion 56 d in the arrow Y direction and the width of thethrough-hole 60 a in the arrow Y direction are almost the same.Therefore, the protrusion portion 56 d is inserted into the through-hole60 a, such that a position of the left upper stay 60 with respect to theleft support column 56 in the arrow Y direction is determined. Inaddition, the step-bent portion 56 e of the left support column 56 isinserted into and engaged with the through-hole 60 b of the left upperstay 60. As a result, the flat surface portion 60 w 1 of the left upperstay 60 is sandwiched from the plate thickness direction (arrow Xdirection) of the flat surface portion 60 w 1 by the step-bent portion56 e and the flat surface portion 56 w 2 in the left support column 56,such that a position of the left upper stay 60 with respect to the leftsupport column 56 in the arrow X direction is determined.

Next, as illustrated in FIG. 24 , the right lower stay 61 is assembled.The right lower stay 61 is a member connecting between the rear sideplate 52 and the right support column 58 facing each other, and isinserted and assembled into the rear side plate 52 and the right supportcolumn 58 from a front side where the right support column 58 islocated, in the horizontal direction (arrow Y direction). The rightlower stay 61 is a member connected to the right support column 58 andthe rear side plate 52 so that an interval between the right supportcolumn 58 and the rear side plate 52 becomes a predetermined interval,and guaranteeing a conveyance property of the sheet S. In addition,since the right lower stay 61 is located in the vicinity of a rightlower corner of the frame 31, the right lower stay 61 has an influenceon rigidity of the frame 31. Therefore, it is particularly desirablethat the right lower stay 61 is assembled with high position accuracy.Hereinafter, an assembly configuration of the right lower stay 61 willbe described in detail.

FIGS. 25A and 25B are perspective views of the right lower stay 61, therear side plate 52, and the right support column 58. Here, FIG. 25Aillustrates a state before the right lower stay 61 is assembled, andFIG. 25B illustrates a state where the right lower stay 61 is assembled.First, an assembly configuration of the right lower stay 61 and the rearside plate 52 will be described. As illustrated in FIGS. 25A and 25B,the flat surface portion 52 a of the rear side plate 52 is provided witha bent portion 250 bent and raised toward the front surface side in thearrow Y direction. The bent portion 250 is bent and raised in a platethickness direction of the flat surface portion 52 a of the rear sideplate 52, and is bent and raised in a direction opposite to the bentportion 52 w with respect to the flat surface portion 52 a. In addition,a through-hole 251 penetrating through the flat surface portion 52 a inthe plate thickness direction (arrow Y direction) of the flat surfaceportion 52 a is formed around the bent portion 250, in the flat surfaceportion 52 a of the rear side plate 52. As described above, the rearside plate 52 is formed of one metal plate, and the through-hole 251 isa hole formed when the bent portion 250 is processed.

The right lower stay 61 includes three flat surfaces and has a U-shapedcross section. The right lower stay 61 has a flat surface portion 61 w 1extending substantially in parallel with the bent portion 52 w of therear side plate 52 and a flat surface portion 61 w 2 bent substantiallyvertically from the flat surface portion 61 w 1 in the arrow X directionat an upper portion of the flat surface portion 61 w 1. In addition, theright lower stay 61 has a flat surface portion 61 w 3 bent so as to facethe flat surface portion 61 w 2 at a lower portion of the flat surfaceportion 61 w 1. The flat surface portion 61 w 1 of the right lower stay61 is provided with a step-bent portion 61 a inserted into and engagedwith the bent portion 250 of the rear side plate 52. The step-bentportion 61 a has a portion bent in the plate thickness direction (arrowX direction) of the flat surface portion 61 w 1 of the right lower stay61 and a portion bent and extended from that portion in the insertiondirection (arrow Y direction) into the rear side plate 52. The step-bentportion 61 a is formed by forming a through-hole around the step-bentportion 61 a at the time of being processed with respect to the flatsurface portion 61 w 2 and bending the step-bent portion 61 a withrespect to the flat surface portion 61 w 2.

When the right lower stay 61 is assembled, the entirety of one endportion of the right lower stay 61 in the arrow Y direction is insertedinto the through-hole 251 of the rear side plate 52, and the step-bentportion 61 a of the right lower stay 61 is inserted into and engagedwith the bent portion 250 of the rear side plate 52. As a result, thebent portion 250 of the rear side plate 52 is sandwiched from the platethickness direction (arrow X direction) of the bent portion 250 by thestep-bent portion 61 a and the flat surface portion 61 w 1 in the rightlower stay 61, such that a position of the right lower stay 61 withrespect to the rear side plate 52 in the arrow X direction (platethickness direction of the flat surface portion 61 w 1) is determined.

In addition, the flat surface portion 61 w 2, which is an upper surfaceof the right lower stay 61, and an inner wall of an upper side of thethrough-hole 251 of the rear side plate 52 face each other with apredetermined interval therebetween, and the flat surface portion 61 w3, which is a lower surface of the right lower stay 61, and an innerwall of a lower side of the through-hole 251 of the rear side plate 52are in contact with each other by a weight of the right lower stay 61.As a result, a position of the right lower stay 61 with respect to therear side plate 52 in the vertical direction (arrow Z direction) isdetermined with a backlash corresponding to a predetermined interval.

Next, an assembly configuration of the right lower stay 61 and the rightsupport column 58 will be described. As illustrated in FIGS. 25A and25B, an insertion hole 58 a into which a step-bent portion 61 b of theright lower stay 61 is inserted is formed in the flat surface portion 58w 2 of the right support column 58. Further, the right support column 58has a flat surface portion (not illustrated) extending in the arrow Ydirection behind the image forming apparatus A from the periphery of theinsertion hole 58 a in the flat surface portion 58 w 2. The flat surfaceportion (not illustrated) is provided with a projection portion (notillustrated) protruding in a plate thickness direction (arrow Xdirection) of the flat surface portion and having a substantiallysemicircular shape. The projection portion (not illustrated) is formedby drawing, and is arranged at a position adjacent to the insertion hole58 a in an insertion direction (arrow Y direction) of the step-bentportion 61 b into the insertion hole 58 a.

In addition, the flat surface portion 61 w 1 of the right lower stay 61is provided with the step-bent portion 61 b inserted into and engagedwith the insertion hole 58 a of the right support column 58. Thestep-bent portion 61 b has a portion bent in the plate thicknessdirection (arrow X direction) of the flat surface portion 61 w 1 and aportion bent and extended from that portion in the insertion direction(arrow Y direction) into the right support column 58.

In addition, a through-hole 61 c penetrating the flat surface portion 61w 1 in the plate thickness direction of the flat surface portion 61 w 1is formed around the step-bent portion 61 b in the flat surface portion61 w 1 of the right lower stay 61. The through-hole 61 c is arranged ata position adjacent to the step-bent portion 61 b in the insertiondirection of the right lower stay 61 into the right support column 58.As described above, the right lower stay 61 is formed of one metalplate, and the through-hole 61 c is a hole formed when the step-bentportion 61 b is processed.

When the right lower stay 61 is assembled, the step-bent portion 61 b ofthe right lower stay 61 is inserted into and engaged with the insertionhole 58 a of the right support column 58, and the projection portion(not illustrated) of the right support column 58 engages with thethrough-hole 61 c of the right lower stay 61. As described above, thestep-bent portion 61 b engages with the insertion hole 58 a, such that aposition of the right lower stay 61 with respect to the right supportcolumn 58 in the arrow X direction, the arrow Y direction, and the arrowZ direction is determined. In addition, an upper surface of thestep-bent portion 61 b and an inner wall of an upper side of theinsertion hole 58 a face each other with a predetermined intervaltherebetween, and a lower surface of the step-bent portion 61 b and aninner wall of a lower side of the insertion hole 58 a face each otherwith a predetermined interval therebetween. As a result, a position ofthe right lower stay 61 with respect to the right support column 58 in adirection from the rear side toward the front side in the arrow Ydirection is determined. With such a configuration, a position of theright lower stay 61 with respect to the right support column 58 in thearrow X direction, the arrow Y direction, and the vertical direction(arrow Z direction) is determined with a backlash corresponding to apredetermined interval.

In addition, in a state where the right lower stay 61 engages with therear side plate 52 or the right support column 58, the projectionportion (not illustrated) of the right support column 58 abuts on theinner wall of the through-hole 61 c, such that movement of the rightlower stay 61 with respect to the rear side plate 52 and the rightsupport column 58 in a direction opposite to the insertion direction isrestricted. The insertion direction of the right lower stay 61 into therear side plate 52 and the right support column 58 is a directionorthogonal to a flat surface of the flat surface portion 52 a of therear side plate 52, and is a direction from the front side toward therear side in the arrow Y direction. The opposite direction to theinsertion direction of the right lower stay 61 into the rear side plate52 and the right support column 58 is a direction orthogonal to a flatsurface of the flat surface portion 52 a of the rear side plate 52, andis a direction from the rear side toward the front side in the arrow Ydirection.

Next, as illustrated in FIG. 26 , the rear side plate 62 is assembled.The rear side plate 62 is inserted and assembled into the rear sideplate 53 from the arrow Z direction. An assembly configuration of therear side plate 62 and the rear side plate 53 is similar to that of therear side plate 52 and the rear side plate 53, and is an assemblyconfiguration in which the rear side plate 62 and the rear side plate 53are inserted into and engaged with each other.

Next, as illustrated in FIGS. 27A and 27B, the right middle stay 65 isassembled. The right middle stay 65 is a plate-shaped member that isformed by one flat surface, and is a member that supports a fan coolingan end portion of the fixing portion 45 in a rotational axis direction.The right middle stay 65 is inserted and assembled into the rear sideplate 53 and the right support column 58. An assembly configuration ofthe right middle stay 65 and the rear side plate 53 and an assemblyconfiguration of the right middle stay 65 and the right support column58 are similar to each other. Therefore, only the assembly configurationof the right middle stay 65 and the rear side plate 53 will be mainlydescribed here.

A through-hole 53 c penetrating the support portion 53 a in the platethickness direction (arrow Y direction) of the support portion 53 a isformed in the support portion 53 a of the rear side plate 53. Note thatthe rear side plate 53 is a member extending in the vertical direction.In addition, the right middle stay 65 is provided with a protrusionportion 65 a protruding in an insertion direction (arrow Y direction)into the support portion 53 a of the rear side plate 53 and insertedinto the through-hole 53 c of the rear side plate 53 from the arrow Ydirection.

The protrusion portion 65 a is provided at a base portion 65 a 1 thatfits into the through-hole 53 c and a tip side in the insertiondirection from the base 65 a 1, and has a hook portion 65 a 2 in whichthe lower end portion 65 a 2 x is located at a position vertically lowerthan the lower end portion 65 a 1 x of the base portion 65 a 1. Inaddition, the protrusion portion 65 a has an inclined portion 65 a 3inclined so that a height decreases from an upper end portion of thebase portion 65 a 1 to an upper end portion of the hook portion 65 a 2.

When the protrusion portion 65 a is inserted into the through-hole 53 c,the hook portion 65 a 2, which is a tip portion of the protrusionportion 65 a, is first inserted, the base portion 65 a 1 is inserted,and the base portion 65 a 1 is then fitted into the through-hole 53 c. Awidth of the base portion 65 a 1 of the protrusion portion 65 a in thevertical direction and a width of the through-hole 53 c in the verticaldirection are substantially the same as each other. In addition, a platethickness of the right middle stay 65 and a width of the through-hole 53c in the arrow X direction are substantially the same as each other.Therefore, the base portion 65 a 1 of the protrusion portion 65 a isfitted into the through-hole 53 c, such that a position of the rightmiddle stay 65 with respect to the rear side plate 53 in the verticaldirection (arrow Z direction) and a position of the right middle staywith respect to the rear side plate in a direction (arrow X direction)orthogonal to the insertion direction and the vertical direction aredetermined.

Further, in the state in which the base portion 65 a 1 of the protrusionportion 65 a is fitted into the through-hole 53 c, a lower end portion65 a 2 x of the hooking portion 65 a 2 is located at a position facingthe portion below the through-hole 53 c in the support portion 53 a ofthe rear side plate 53. In the present embodiment, the lower end portion65 a 2 x of the hook portion 65 a 2 protrudes 2 mm downward with respectto the lower end portion 65 a 1 x of the base portion 65 a 1 and isprovided so as to be spaced by 3 mm from the facing portion of the rightmiddle stay facing the support portion 53 a of the rear side plate 53.Here, the plate thickness of the support portion 53 a of the rear sideplate 53 is about 1 mm, and the length of the base portion 65 a 1 of theprotrusion portion 65 a in the arrow Y direction is longer than theplate thickness of the support portion 53 a of the rear side plate 53.As a result, even though the rear side plate 53 and the right middlestay 65 are relatively inclined during assembly, the hook portion 65 a 2is hooked on the support portion 53 a, such that movement of the rightmiddle stay 65 with respect to the support portion 53 a of the rear sideplate 53 in a direction opposite to the insertion direction isrestricted. Therefore, the right middle stay 65 is prevented from beingseparated from the rear side plate 53, such that it is possible toassemble the right middle stay 65 and the rear side plate 53 to eachother with high position accuracy. In addition, since the assemblyconfiguration of the right middle stay 65 and the rear side plate 53 andthe assembly configuration of the right middle stay 65 and the rightsupport column 58 are the same as each other as described above, theright middle stay 65 is prevented from being separated from the rightsupport column 58, such that it is possible to improve position accuracyof the right middle stay 65 and the right support column 58.

Next, as illustrated in FIG. 28 , the right support column 63 isassembled. The right support column 63 faces the flat surface portion 63w 1 extending parallel to the flat surface portion 55 w 1 of the frontside plate 55, the flat surface portion 63 w 2 bent substantiallyperpendicular to the arrow Y direction from the flat surface portion 63w 1, and a flat surface portion 63 w 3 bent substantially vertically soas to face the flat surface portion 63 w 1 from the flat surface portion63 w 2. The right support column 63 and the right support column 58 areinserted and assembled into each other.

FIGS. 29A and 29B are enlarged perspective views of an engaging portionbetween the right support column 63 and the right support column 58.Here, FIG. 29A illustrates a state before the right support column 63and the right support column 58 are assembled to each other, and FIG.29B illustrates a state where the right support column 63 and the rightsupport column 58 are assembled to each other.

As illustrated in FIGS. 29A and 29B, the flat surface portion 63 w 2 ofthe right support column 63 is provided with a projection portion 63 aprotruding in a plate thickness direction (arrow X direction) of theflat surface portion 63 w 2 and two protrusion portions 63 b protrudingin an insertion direction (arrow Z direction) into the right supportcolumn 58. Here, the protrusion portion 63 b is provided below theprojection portion 63 a in the vertical direction (arrow Z direction).The projection portion 63 a is formed by drawing, and the amount ofprotrusion from the surface of the flat surface portion 63 w 2 is about0.3 mm to 2 mm. In addition, a tip portion of the protrusion portion 63b is an inclined portion 63 b 1 inclined in a direction away from theflat surface portion 63 w 2 with respect to the insertion direction ofthe right support column 63 into the right support column 58.

The flat surface portion 58 w 2 of the right support column 58 isprovided with a step-bent portion 58 c protruding in an insertiondirection (arrow Z direction) of the right support column 58 into theright support column 63. In addition, a through-hole 58 d penetratingthe flat surface portion 58 w 2 in a plate thickness direction (arrow Xdirection) of the flat surface portion 58 w 2 is formed at a positionadjacent to the step-bent portion 58 c in the insertion direction of theright support column 58 with respect to the right support column 63. Thestep-bent portion 58 c has a portion bent in the plate thicknessdirection of the flat surface portion 58 w 2 and a portion bent andextended from that portion in the insertion direction into the rightsupport column 63. In addition, a tip portion of the step-bent portion58 c is an inclined portion 58 c 1 inclined in a direction away from theflat surface portion 58 w 2 with respect to the insertion direction ofthe right support column 58 into the right support column 63.

When the right support column 63 is assembled to the right supportcolumn 58, the inclined portion 58 c 1 of the step-bent portion 58 c ofthe right support column 58 abuts on the flat surface portion 63 w 2 ofthe right support column 63, and the inclined portion 63 b 1 of theprotrusion portion 63 b of the right support column 63 abuts on the flatsurface portion 58 w 2 of the right support column 58. As a result,movement of the right support column 63 and the right support column 58in the arrow Z direction is guided, and the flat surface portion 63 w 2and the flat surface portion 58 w 2 move in a predetermined positionalrelationship. In addition, a lower end portion of a stopper portion 63 cof the right support column 63 butts a butting portion 58 e, which is anupper end portion of the flat surface portion 58 w 2 of the rightsupport column 58, such that movement of the right support column 63with respect to the right support column 58 in the insertion direction(arrow Z direction) is restricted.

When the right support column 63 is assembled to the right supportcolumn 58, the step-bent portion 58 c of the right support column 58 isinserted into the flat surface portion 63 w 2 of the right supportcolumn 63 and engages with a lower end portion of the flat surfaceportion 63 w 2. As a result, the flat surface portion 63 w 2 of theright support column 63 is sandwiched from the plate thickness direction(arrow X direction) of the flat surface portion 63 w 2 by the step-bentportion 58 c and the flat surface portion 58 w 2 in the right supportcolumn 58, such that a position of the right support column 63 withrespect to the right support column 58 in the arrow X direction isdetermined.

In addition, the projection portion 63 a of the right support column 63engages with the through-hole 58 d formed in the right support column58. As a result, an edge portion 63 a 1 of the projection portion 63 aabuts on an inner wall of the through-hole 58 d, such that movement ofthe right support column 58 with respect to the right support column 63in a direction opposite to the insertion direction is restricted. Here,the through-hole 58 d is arranged at a position adjacent to thestep-bent portion 58 c in the insertion direction of the right supportcolumn 58 into the right support column 63. Therefore, the projectionportion 63 a engaged with the through-hole 58 d and the step-bentportion 58 c are arranged at positions adjacent to each other in theinsertion direction.

A configuration in which the edge portion 63 a 1 of the projectionportion 63 a abuts on the inner wall of the through-hole 58 d formedwhen the step-bent portion 58 c is processed has been described in thepresent embodiment, but a configuration in which the edge portion 63 a 1of the projection portion 63 a abuts on an inner wall of anotherthrough-hole different from the through-hole 58 d may be adopted. As aresult, the movement of the right support column 63 with respect to theright support column 58 in the direction opposite to the insertiondirection is restricted.

In addition, in a direction (arrow Y direction) orthogonal to the platethickness direction of the flat surface portion 63 w 2 and the insertiondirection into the right support column 58, the two protrusion portions63 b of the right support column 63 engage with the step-bent portion 58c so as to sandwich the step-bent portion 58 c of the right supportcolumn 58 therebetween. As a result, a position of the right supportcolumn 63 with respect to the right support column 58 in the orthogonaldirection is determined.

As described above, the projection portion 63 a restricting the movementof the right support column 63 with respect to the right support column58 in the direction opposite to the insertion direction is provided inthe vicinity of the step-bent portion 58 c engaging the flat surfaceportion 63 w 2 of the right support column 63 and the flat surfaceportion 58 w 2 of the right support column 58 with each other. As aresult, it is possible to prevent the right support column 63 frommoving with respect to the right support column 58 in the directionopposite to the insertion direction, such that the right support column63 and the right support column 58 are separated from each other,resulting in deterioration of position accuracy. Therefore, the rightsupport column 63 and the right support column 58 that constitute theframe 31 can be assembled to each other with high position accuracy.

Next, as illustrated in FIGS. 30A and 30B, the right upper stay 64 isassembled. The right upper stay 64 has a flat surface portion 64 w 1extending in the horizontal direction, a flat surface portion 64 w 2formed by bending one end portion of the flat surface portion 64 w 1 inthe arrow X direction substantially vertically in the verticaldirection, and a flat surface portion 64 w 3 formed by bending one endportion of the flat surface portion 64 w 1 in the arrow Y directionsubstantially vertically in the vertical direction. In addition, theright upper stay 64 has a flat surface portion (not illustrated) formedby bending the other end portion of the flat surface portion 64 w 1 inthe arrow Y direction substantially vertically in the verticaldirection. The right upper stay 64, and the rear side plate 62 and theright support column 63 are inserted and assembled into with each other.An assembly configuration of the right upper stay 64 and the rear sideplate 62 and an assembly configuration of the right upper stay 64 andthe right support column 63 are similar to each other. Therefore, onlythe assembly configuration of the right upper stay 64 and the rightsupport column 63 will be described here.

The flat surface portion 64 w 3 of the right upper stay 64 includesthree bent portions 304 a, 304 b, and 304 c bent from the flat surfaceportion 64 w 1 in an insertion direction (arrow Z direction) into theright support column 63. That is, when the flat surface portion 64 w 3is divided into three portions in the arrow X direction, there are thebent portions 304 a, 304 b, and 304 c. The bent portion 304 c isarranged at a position between the bent portion 304 a and the bentportion 304 b in the arrow X direction, and a length of the bent portion304 c in the arrow Z direction is smaller than that of the bent portions304 a and 304 b in the arrow Z direction. In addition, the bent portions304 a and 304 b have the same length in the arrow Z direction, and tipportions of the bent portions 304 a and 304 b are inclined portions 304a 1 and 304 b 1 inclined in a direction away from the flat surfaceportion 64 w 1 with respect to the insertion direction into the rightsupport column 63.

In addition, the flat surface portion 63 w 3 of the right support column63 is provided with a step-bent portion 316 protruding in an insertiondirection (vertical direction and arrow Z direction) into the rightupper stay 64 and inserted into and engaged with the right upper stay 64so as to overlap with the bent portion 304 c of the right upper stay 64in a plate thickness direction (arrow Y direction) of the flat surfaceportion 63 w 3. In addition, the flat surface portion 63 w 2 of theright support column 63 is provided with a step-bent portion 325protruding in the insertion direction into the right upper stay 64 andinserted into and engaged with the flat surface portion 64 w 2 so as tooverlap with the flat surface portion 64 w 2 of the right upper stay 64in a plate thickness direction (arrow X direction) of the flat surfaceportion 63 w 2. In addition, the flat surface portion 63 w 2 of theright support column 63 is provided with a projection portion 330penetrating the flat surface portion 63 w 2 in a plate thicknessdirection (arrow X direction) of the flat surface portion 63 w 2.

The step-bent portion 316 has a portion bent in the plate thicknessdirection (arrow Y direction) of the flat surface portion 63 w 3 of theright support column 63 and a portion bent and extended from thatportion in the insertion direction (arrow Z direction) into the rightupper stay 64. In addition, a tip portion of the step-bent portion 316is an inclined portion 316 a formed by further bending a portion of thestep-bent portion 316 bent in the insertion direction into the rightupper stay 64 and inclined in a direction away from the flat surfaceportion 63 w 3 with respect to the insertion direction into the rightupper stay 64.

The step-bent portion 325 has a portion bent in the plate thicknessdirection (arrow X direction) of the flat surface portion 63 w 2 of theright support column 63 and a portion bent and extended from thatportion in the insertion direction (arrow Z direction) into the rightupper stay 64. In addition, a tip portion of the step-bent portion 325is an inclined portion 325 a formed by further bending a portion of thestep-bent portion 325 bent in the insertion direction into the rightupper stay 64 and inclined in a direction away from the flat surfaceportion 63 w 2 with respect to the insertion direction into the rightupper stay 64.

When the right upper stay 64 is assembled to the right support column63, the inclined portions 316 a and 325 a of the step-bent portions 316and 325 of the right support column 63 abut on the right upper stay 64,and the inclined portion 304 a 1 and 304 b 1 of the bent portions 304 aand 304 b of the right upper stay 64 abut on the right support column63. As a result, movement of the right upper stay 64 and the rightsupport column 63 is guided, such that the right upper stay 64 and theright support column 63 move in a predetermined positional relationship.

When the step-bent portion 316 engages with the bent portion 304 c ofthe right upper stay 64 and the bent portions 304 a and 304 b engagewith the flat surface portion 63 w 3 of the right support column 63, thestep-bent portion 316 and the bent portions 304 a and 304 b alternatelyperform engagement in a direction (arrow X direction) orthogonal to theinsertion direction of the right support column 63 into the right upperstay 64 and the plate thickness direction. Specifically, the bentportion 304 a engages with the flat surface portion 63 w 3 of the rightsupport column 63 at a position adjacent to the step-bent portion 316 inthe arrow X direction. In addition, the bent portion 304 b engages withthe flat surface portion 63 w 3 of the right support column 63 on a sideopposite to a side where the bent portion 304 a is arranged, withrespect to the step-bent portion 316, and at a position adjacent to thestep-bent portion 316, in the arrow X direction. With such aconfiguration, the right upper stay 64 and the right support column 63are firmly engaged with and assembled to each other.

In addition, the projection portion 330 of the right support column 63engages with a through-hole 335 formed in the flat surface portion 64 w2 of the right upper stay 64 and penetrating the flat surface portion 64w 2 in a plate thickness direction (arrow X direction) of the flatsurface portion 64 w 2. As a result, an edge portion 330 a of theprojection portion 330 abuts on an inner wall of the through-hole 335,such that movement of the right upper stay 64 with respect to the rightsupport column 63 in a direction opposite to the insertion direction isrestricted.

As described above, the respective metal plates constituting the frame31 are assembled. The frame 31 assembled in the assembling process asdescribed above is configured to be able to stand for oneself.Therefore, the frame 31 can be detached from the stand 33 by graspingthe rear side plate 52, the left support column 56, the right supportcolumn 58, and the like, of the frame 31 and lifting the frame 31.

<Joining Process of Frame>

Next, a process of joining the frame 31 assembled in the assemblingprocess described above will be described.

FIG. 31 is a perspective view of a jig 34 used for joining of the frame31. As illustrated in FIGS. 29A and 29B, the jig 34 has a base 34 a, afront side support portion 34 b, and a rear side support portion 34 c.The base 34 a is provided with a positioning pin 34 a 1. In addition,the front side support portion 34 b and the rear side support portion 34c are configured to be slidable with respect to the base 34 a. The frontside support portion 34 b slides in the directions of arrows K1 and K2,and the rear side support portion 34 c slides in the directions ofarrows K3 and K4.

FIG. 32 is a perspective view of the frame 31 assembled in theassembling process described above and the jig 34. As illustrated inFIGS. 30A and 30B, the frame 31 is detached from the stand 33 and placedon the base 34 a of the jig 34 after the assembling process. At thistime, the positioning pins 34 a 1 of the base 34 a are inserted into thepositioning holes 51 a of the rear bottom plate 51 of the frame 31 orthe positioning holes 57 b of the front lower stay 57, such that aposition of the frame 31 with respect to the base 34 a is determined.

As illustrated in FIG. 33 , when joining the frame 31, an operator whoperforms a joining process slides the front side support portion 34 b inthe arrow K1 direction and slides the rear side support portion 34 c inthe arrow K3 direction. In addition, the frame 31 is pressed from adirection orthogonal to slide directions of the front side supportportion 34 b and the rear side support portion 34 c and the verticaldirection by a pressing device (not illustrated). As a result, the metalplates constituting the frame 31 are pressed against each other, suchthat unnecessary gaps between the metal plates are eliminated, andpositioning is completed.

Then, the respective metal plates constituting the frame 31 are joinedto each other by fiber laser welding by the operator. When the joiningof the frame 31 is completed, the operator slides the front side supportportions 34 b in the arrow K2 direction, slides the rear side supportportions 34 c in the arrow K4 direction, and detaches the frame 31 fromthe jig 34. As a result, the frame 31 is completed.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2020-154963, filed Sep. 15, 2020, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A metal frame of an image forming apparatus,comprising: a first support configured to support one end of an imageforming unit that forms an image on a sheet, the first support includinga first metal plate and a second metal plate which supports the firstmetal plate below the first metal plate in a vertical direction; asecond support which is spaced apart from the first support andconfigured to support the other end of the image forming unit; and athird support configured to connect the first support and the secondsupport to each other, wherein the first metal plate includes: a firstportion, and a second portion which is bent substantially verticallyfrom the first portion, and including a substantially right-angledcorner portion being provided between the first portion and the secondportion, wherein the second metal plate includes: a third portion, afourth portion which is bent substantially vertically upward in thevertical direction from an end portion in a first direction orthogonalto the vertical direction in the third portion, and engages with and isassembled to the first portion, and a fifth portion which is bentsubstantially vertically upward in the vertical direction from an endportion in a second direction orthogonal to the vertical direction andthe first direction in the third portion, and engages with and isassembled to the second portion, wherein the fifth portion includes afirst stretched portion which extends along the end portion in thesecond direction with respect to the third portion and a secondstretched portion which is bent substantially vertical with respect tothe first stretched portion and extends along the second direction,another corner portion located between the first stretched portion andthe second stretched portion facing the corner portion of the firstmetal plate, and wherein a tip of the second stretched portion faces thefourth portion.
 2. The metal frame of an image forming apparatusaccording to claim 1, wherein the fourth portion includes a thirdstretched portion which extends along the end portion in the firstdirection with respect to the third portion, and a fourth stretchedportion which is bent substantially vertically from the third stretchedportion and extends along the first direction, and the fourth stretchedportion faces the tip of the second stretched portion.
 3. The metalframe of an image forming apparatus according to claim 1, wherein thefirst portion includes a first engaging portion which engages with thefourth portion, the first engaging portion includes a first bent portionwhich is bent in a plate thickness direction of the first portion and asecond bent portion which is bent to extend in the vertical directionfrom the first bent portion toward the fourth portion, the firstengaging portion engaging with the fourth portion such that the firstportion and the second bent portion sandwich the fourth portion, and thesecond portion includes a second engaging portion which engages with thefifth portion, and includes a third bent portion which is bent in aplate thickness direction of the second portion and a fourth bentportion which is bent to extend in the vertical direction from the thirdbent portion toward the fifth portion, the second engaging portionengaging with the fifth portion such that the second portion and thefourth bent portion sandwich the fifth portion.
 4. The metal frame of animage forming apparatus according to claim 1, wherein a gap between thetip of the second stretched portion and the fourth portion is equal toor less than a plate thickness of the first metal plate.
 5. The metalframe of an image forming apparatus according to claim 1, wherein thefirst support includes a first side plate which supports the imageforming unit, a second side plate configured to support the first sideplate below the first side plate, and a bottom plate configured tosupport the second side plate below the second side plate, the secondsupport includes a third side plate which supports the image formingunit with the first side plate, a first support column configured tosupport one end side in a direction orthogonal to a vertical directionand a plate thickness direction of the third side plate in the thirdside plate, and a second support column configured to support the otherend side in the direction orthogonal to the vertical direction and theplate thickness direction of the third side plate in the third sideplate, and the first metal plate is the second side plate, and thesecond metal plate is the bottom plate.
 6. A metal frame of an imageforming apparatus, comprising: a first support configured to support oneend of an image forming unit that forms an image on a sheet, the firstsupport including a first metal plate and a second metal plateconfigured to support the first metal plate below the first metal platein a vertical direction; a second support which is spaced apart from thefirst support and configured to support the other end of the imageforming unit; and a third support configured to connect the firstsupport and the second support to each other, wherein the first metalplate includes: a first portion, and a second portion which is bentsubstantially vertically from the first portion, and including asubstantially right-angled corner portion being provided between thefirst portion and the second portion, wherein the second metal plateincludes: a third portion which is arranged vertically below the firstportion, a fourth portion which is bent substantially vertically fromthe third portion and is arranged below the second portion in thevertical direction, a fifth portion which is bent from an upper portionof the third portion to form a step with the third portion in a platethickness direction of the third portion, and engages with and isassembled to the first portion, and a sixth portion which is bent froman upper portion of the fourth portion to form a step with the fourthportion in a plate thickness direction of the fourth portion, andengages with and is assembled to the second portion, wherein the sixthportion includes a first stretched portion which extends along a firstdirection orthogonal to the vertical direction, and a second stretchedportion which is bent substantially vertical with respect to the firststretched portion and extends along a second direction orthogonal to thevertical direction and the first direction, another corner portionlocated between the first stretched portion and the second stretchedportion facing the corner portion of the first metal plate, and whereina tip portion of the second stretched portion faces the fifth portion.7. The metal frame of an image forming apparatus according to claim 6,wherein the sixth portion includes a third stretched portion whichextends along the second direction and a fourth stretched portion whichis bent substantially vertical to the third stretched portion andextends along the first direction, and the fourth stretched portionfaces a tip of the second stretched portion.
 8. The metal frame of animage forming apparatus according to claim 6, wherein the first portionincludes a first engaging portion which engages with the fifth portion,the first engaging portion including a first bent portion which is bentin a plate thickness direction of the first portion and a second bentportion which is bent to extend in the vertical direction from the firstbent portion toward the fifth portion, the first engaging portionengaging with the fifth portion such that the first portion and thesecond bent portion sandwich the fifth portion, and the second portionincludes a second engaging portion which engages with the sixth portion,the second engaging portion including a third bent portion which is bentin a plate thickness direction of the second portion and a fourth bentportion which is bent to extend in the vertical direction from the thirdbent portion toward the fifth portion, the second engaging portionengaging with the sixth portion such that the second portion and thefourth bent portion sandwich the sixth portion.
 9. The metal frame of animage forming apparatus according to claim 6, wherein a gap between thetip of the second stretched portion and the fifth portion is equal to orless than a plate thickness of the first metal plate.
 10. The metalframe of an image forming apparatus according to claim 6, wherein thefirst metal plate supports the image forming unit, and the secondsupport includes a side plate which supports the image forming unittogether with the first metal plate, a first support column configuredto support one end side in a direction orthogonal to a verticaldirection and a plate thickness direction of the side plate in the sideplate, and a second support column configured to support the other endside in the direction orthogonal to the vertical direction and the platethickness direction of the side plate in the side plate.
 11. An imageforming apparatus, comprising: an image forming unit which forms animage on a sheet; the metal frame of the image forming apparatusaccording to claim 1, the metal frame supporting the image forming unit;and an outer cover configured to cover the metal frame.
 12. An imageforming apparatus, comprising: an image forming unit configured to forman image on a sheet; the metal frame of the image forming apparatusaccording to claim 6, the metal frame supporting the image forming unit;and an outer cover configured to cover the metal frame.